One method for utilising plasterboard has been to fasten the plasterboard into position and then cover its exposed face and the joints between plasterboard sheets with a thin “skim coat” of wet plaster. After this has set, it requires decoration with paint or wallpaper.
Another method for utilising plasterboard has been widely used and dispenses with the “skim coat”. The plasterboard is manufactured using a plasterboard liner paper which has a light colour. This is used to form the front surface and the side edge surfaces. The side edges of the boards are shaped to form a recess at their abutting edges. After the boards are fastened into position, their abutting edges are joined with tape and a jointing compound which is worked into the recess on top of the joining tape to create a continuous flat wall surface, with joints visible at regular intervals. The wall is then decorated, either with wallpaper or with multiple coats of paint, which serves among other things to conceal the joints. If paint is used, the normal requirement is a first “mist coat” or primer, followed by two full further coats. This requires painters to come to the wall three times.
There have been a number of proposals for the manufacture of plasterboard with a decorative finish applied during manufacture, prior to fixing the boards in place. Examples of such proposals include U.S. Pat. Nos. 3,507,684, 3,694,298 and 3,984,596.
U.S. Pat. No. 4,579,610 proposed a process in which the surface of a plasterboard liner paper is gravure printed with a clear or tinted latex base coat in a pattern of dots, so that the applied material does not seal the paper. The base paper is then overprinted with a decorative design. This decorative design is not described in detail although it is said that a pattern of blotches is preferred.
Of course, if the surface of the plasterboard is pre-decorated in some way, there can still be a contrast between the boards and a jointing compound which is applied at the joints between boards.
WO 99/57371 discloses lining paper which is given a coating before being made into plasterboard. The coated surface is said to be suitable to receive flexographic printing and there is a suggestion to print a decorative pattern of speckles. The plasterboards may be used as ceiling tiles. Joints between them are not mentioned.
EP-A-521804 (Lafarge) has described plasterboard manufactured using a liner paper with a coating applied to the liner paper before the boards are manufactured. The document recognises that it is desirable to avoid contrast between the colour of the board and the colour of material used to form joints between the boards.
EP-A-1076137 (BPB plc) discloses plasterboard lining paper pre-decorated by printing over its whole surface, with a layer of applied print which appears continuous when inspected by eye. The colour of the print may be matched to the colour of jointing compound. Jointing compounds have been described in a number of documents.
GB-A-1265804 (BPB Industries) discloses a composition containing ground limestone, talc, mica and vinyl copolymer binder. It also teaches addition of small percentages of bentonite clay and cellulose ether.
GB-A-2048235 (BPB Industries) discloses a jointing compound containing gypsum plaster of particle size less than 150 μm, inert mineral filler of particle size 100 μm and polymeric binder which may be polyvinyl alcohol or starch. The mineral filler may be ground limestone, and the exemplified composition includes a small percentage of bentonite.
Both these documents mention that pigment may be included in jointing compounds. GB-A-2048235 mentions that the added colour may serve to match the colour of the facing paper of plasterboard.
Kanuf Bauprodukte GmbH sell moisture resistant grades of plasterboard with a distinctive green surface, and an accompanying jointing compound which is also coloured green to match the board.
WO 97/02395 (Lafarge) discloses a jointing compound intended to match the surface of pre-decorated plasterboard, made using a lining paper with a coated surface, according to EP-A-521804 (Lafarge). This WO 97/02395 teaches that the jointing compound should contain a high proportion of filler which has a particle size of 5 to 35 micrometers. The proprietors of WO 97/02395, Lafarge, sell pre-decorated boards and a jointing compound of matching colour.
Thus it is known to be desirable to match the appearance of the pre-decorated board surface and the jointing compound used with the boards.
We have now observed that when boards are made with pre-decorated lining paper as taught in EP-A-1076137 and joined with a conventional jointing compound, with a good match between the colour of the boards and the jointing compound, there may still be an observable contrast between the surface of the boards and the exposed surface of the jointing compound. It can be described as a visible difference in the texture of the two surfaces.